This invention is concerned with glass moulding apparatus comprising a first support arranged to support one or more mould portions, a second support arranged to support an equal number of mould portions as the first support, and mould opening and closing means operable to move the supports towards one another into closed positions thereof, in which each mould portion on each support engages a mould portion supported on the other support and cooperates in defining a mould cavity in which molten glass can be moulded, the mould opening and closing means also beign operable to move the supports away from one another into open positions thereof so that the mould portions are separated to allow moulded glass to be removed from the mould cavity. Such glass moulding apparatus is used in glassware forming machines particularly glassware forming machines of the Individual Section, or I.S., type.
A glassware forming machine of the I.S. type has a plurality of sections each of which operates to mould molten gobs of glass into completed glass containers. The sections are arranged to receive gobs from a common source and operate cyclically with phase differences between the various sections. Each section has a blank station at which gobs are moulded into an intermediate shape, known as a parison, and a finish station at which parisons moulded at the blank station are moulded into completed containers. A section has glass moulding apparatus as described above at its blank station to provide a mould cavity in which parisons are moulded and at its finish station to provide a mould cavity in which containers are moulded. In conventional glass moulding apparatus, the first and second supports are provided by arms that are either pivotally mounted on a common vertical pivot pin or, in the A.I.S. type of machine, are linearly movable on guide rods. One, two, three or four mould side portions are hung on each arm to cooperate with side portions on the other arm in forming mould cavities. The mould opening and closing means comprises a pneumatic or hydraulic piston and cylinder assembly acting through a system of links to pivot the arms in opposite directions about the pivot pin or, in the A.I.S. type of machine, to move the supports along the guide rods.
In the above-described conventional glass moulding apparatus, the mould portions are held in their engaged position by the action of the pneumatic piston and cylinder assembly. However, this assembly is unable in some cases to apply sufficient pressure to prevent the mould portions forming a cavity from separating slightly with a consequent detrimental effect on the parison or container being moulded. For example, when containers are being moulded by the press-blow process in which the parison is mouldedby a pressing operation at the blank station and the parison is blown into a container at the finish station, the gob of molten glass is introduced into the mould cavity at the blank station and a plunger is pushed into the cavity to press the glass into conformity with the shape of the cavity. The force with which the plunger is pushed into the mould cavity has to be sufficient for good moulding but tends to force the mould portions apart causing "seams" to be formed in the parison along the contact-line of the mould portions.
As an example, in the production of beer bottles on a conventional I.S. machine with three moulds at each station of each section (a triple-gob process) using the press-blow process with a 0.79 inch (20 mm) diameter plunger, the pressure applied to each plunger would be approximately 15 lbf/sq.in (100 kPa) which causes a force along the centre-line of the centre mould of approximately 3370 lbf (15 kN) tending to force the supports apart. The mould opening and closing means can apply only about 2700 lbf (12 kN) but this is assisted by the effects of bearing play, deflection of the arms and torsional deflection of the linkage. The result is that the mould portions are not firmly held together.
The problem of holding the mould portions firmly together has been recognised and attempts made to solve it. U.S. Pat. Nos. 4,375,979 and 3,528,796 and GB Patent Specification No. 1207669 describe various proposals for solving this problem but these proposals are inefficient as they involve applying clamping forces which are not aligned with the mould portions.
It is an object of the present invention to provide a glass moulding apparatus in which a clamping force aligned with the mould portions can be applied to hold the mould portions in their closed positions.